System and method for inhibiting uncontrolled regeneration of a particulate filter for an internal combustion engine

ABSTRACT

A NOx adsorber catalyst may comprise a housing defining an inlet configured to receive exhaust gas produced by an internal combustion engine, an outlet and a chamber between the inlet and the outlet. A NOx adsorber element may be positioned in the chamber adjacent to the inlet. The NOx adsorber element may be configured to trap NOx in the exhaust gas during lean fuel operation of the engine, and to release the trapped NOx and reduce the released NOx to nitrogen during rich fuel operation of the engine. A hydrocarbon trap may be positioned in the chamber between the NOx adsorber element and the outlet. The hydrocarbon trap may be configured to trap hydrocarbons that travel through the NOx adsorber element during the rich fuel operation of the engine. The trapped hydrocarbons may be oxidized by oxygen present in the exhaust gas during lean fuel operation following rich fuel operation.

FIELD OF THE INVENTION

The present invention relates generally to exhaust gas aftertreatmentcomponents, and more specifically to the systems and devices forprocessing NOx present in exhaust gas produced by an internal combustionengine.

BACKGROUND

NOx adsorber catalysts for processing NOx present in exhaust gasproduced by internal combustion engines are generally known. It isdesirable to minimize, or at least reduce, the passage of hydrocarbonsthrough such exhaust gas aftertreatment devices during rich fuelconditions typically associated with device regeneration events.

SUMMARY

The present invention may comprise one or more of the features recitedin the attached claims, and/or one or more of the following features andcombinations thereof. A NOx adsorber catalyst may comprise a housingdefining an inlet at one end configured to receive exhaust gas producedby an internal combustion engine, an outlet at an opposite end and achamber between the inlet and the outlet. A NOx adsorber element may bepositioned in the chamber adjacent to the inlet of the housing. The NOxadsorber element may be configured to trap NOx in the exhaust gas duringlean fuel operation of the engine, and to release the trapped NOx andreduce the released NOx to nitrogen during rich fuel operation of theengine. A hydrocarbon trap may be positioned in the chamber between theNOx adsorber element and the outlet of the housing. The hydrocarbon trapmay be configured to trap hydrocarbons that travel through the NOxadsorber element during the rich fuel operation of the engine. Thetrapped hydrocarbons are oxidized by oxygen present in the exhaust gasduring lean fuel operation of the engine following rich fuel operation.

The hydrocarbon trap may be integral with the NOx adsorber element.Alternatively, the hydrocarbon trap may be attached to the NOx adsorberelement. Alternatively still, the hydrocarbon trap may be spaced apartfrom the NOx adsorber element within the chamber of the housing.

The hydrocarbon trap may comprise a substrate wash-coated withzeolite-containing material.

A NOx adsorber catalyst may comprise a housing defining an inlet at oneend configured to receive exhaust gas produced by an internal combustionengine, an outlet at an opposite end and a chamber between the inlet andthe outlet. A NOx adsorber element may be positioned in the chamber. TheNOx adsorber element may include a first portion adjacent to the inletof the housing and a second portion integral with the first portion withthe first portion positioned between the inlet of the housing and thesecond portion. The first portion of the NOx adsorber element may beconfigured to trap NOx in the exhaust gas during lean fuel operation ofthe engine, and to release the trapped NOx and reduce the released NOxto nitrogen during rich fuel operation of the engine. The second portionof the NOx adsorber element may be configured to trap hydrocarbons thattravel through the first portion during the rich fuel operation of theengine. The trapped hydrocarbons may be oxidized by oxygen present inthe exhaust gas during lean fuel operation of the engine following richfuel operation.

A NOx adsorber catalyst may comprise a housing defining an inlet at oneend configured to receive exhaust gas produced by an internal combustionengine, an outlet at an opposite end and a chamber between the inlet andthe outlet. A NOx adsorber element may be positioned in the chamberadjacent to the inlet of the housing. The NOx adsorber element may beconfigured to trap NOx in the exhaust gas during lean fuel operation ofthe engine, and to release the trapped NOx and reduce the released NOxto nitrogen during rich fuel operation of the engine. A hydrocarbontrap, separate from the NOx adsorber element, may be positioned in thechamber between the NOx adsorber element and the outlet of the housing.The hydrocarbon trap may be configured to trap hydrocarbons that travelthrough the NOx adsorber element during the rich fuel operation of theengine. The trapped hydrocarbons may be oxidized by oxygen present inthe exhaust gas during lean fuel operation of the engine following richfuel operation. The hydrocarbon trap may be attached to the NOx adsorberelement. Alternatively, the hydrocarbon trap may be spaced apart fromthe NOx adsorber element within the chamber of the housing.

A system for processing NOx present in exhaust gas produced by aninternal combustion engine may comprise a NOx adsorber catalyst havinghousing defining an inlet at one end that is configured to receive theexhaust gas, an outlet at an opposite end and a chamber between theinlet and the outlet. A NOx adsorber element may be positioned in thechamber adjacent to the inlet of the housing. The NOx adsorber elementmay be configured to trap NOx in the exhaust gas during lean fueloperation of the engine, and to release the trapped NOx and reduce thereleased NOx to nitrogen during rich fuel operation of the engine. Ahydrocarbon trap may be positioned in the chamber between the NOxadsorber element and the outlet of the housing. The hydrocarbon trap maybe configured to trap hydrocarbons that travel through the NOx adsorberelement during the rich fuel operation of the engine. A fuel system maybe configured to supply fuel to the engine. A control circuit mayinclude a memory having stored therein a set of instructions that areexecutable by the control circuit to control the fuel system to normallysupply fuel for lean fuel operation of the engine, and to control thefuel system to supply fuel for alternate rich fuel operation of theengine and lean fuel operation of the engine to regenerate the NOxadsorber. The hydrocarbons trapped in the hydrocarbon trap may beoxidized by oxygen present in the exhaust gas during lean fuel operationof the engine following rich fuel operation.

The system may further comprise an oxidation catalyst positioned betweenthe engine and the NOx adsorber. The instructions stored in the memorymay include instructions that are executable by the control circuit tocontrol the fuel system to introduce hydrocarbons in the form ofunburned or partially burned fuel into the exhaust gas duringregeneration of the NOx adsorber. The oxidation catalyst may react withthe introduced hydrocarbons to heat the exhaust gas supplied to the NOxadsorber to an elevated temperature suitable for regeneration of the NOxadsorber.

The hydrocarbon trap may be integral with the NOx adsorber element.Alternatively, the hydrocarbon trap may be attached to the NOx adsorberelement. Alternatively still, the hydrocarbon trap may be spaced apartfrom the NOx adsorber element within the chamber of the housing.

The hydrocarbon trap may comprise a substrate wash-coated withzeolite-containing material.

The system may further comprise an oxygen sensor configured to producean oxygen signal corresponding to an oxygen concentration of exhaust gasexiting the NOx adsorber catalyst. The instructions stored in the memoryinclude instructions that are executable by the control circuit tocontrol the fuel system to supply fuel for alternate rich fuel operationof the engine and lean fuel operation of the engine to regenerate theNOx adsorber according to a closed-loop control strategy as a functionof the oxygen concentration of exhaust gas exiting the NOx adsorbercatalyst.

The system may further comprise means for determining an oxygenconcentration of exhaust gas entering the NOx adsorber catalyst. Theinstructions stored in the memory include instructions that areexecutable by the control circuit to control the fuel system to supplyfuel for alternate rich fuel operation of the engine and lean fueloperation of the engine to regenerate the NOx adsorber according to theclosed-loop control strategy further as a function of the oxygenconcentration of exhaust gas entering the NOx adsorber catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bock diagram of a closed-loop control system for controllingoperation of a NOx adsorber catalyst in an exhaust gas aftertreatmentsystem for an internal combustion engine.

FIG. 2 is a cross section of one embodiment of the NOx adsorber catalystof FIG. 1.

FIG. 3 is a cross section of another embodiment of the NOx adsorbercatalyst of FIG. 1.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to a number of illustrativeembodiments shown in the attached drawings and specific language will beused to describe the same.

Referring now to FIG. 1, one illustrative embodiment of a closed-loopcontrol system 10 is shown for controlling regeneration of a NOxadsorber catalyst 36 in an exhaust gas aftertreatment system for aninternal combustion engine 12. In the illustrated embodiment, the system10 includes an internal combustion engine 12 having an intake manifold14 fluidly coupled to a fresh air outlet of a compressor 16 of aturbocharger 18 via a conduit 20. A fresh air inlet of the compressor 16is fluidly coupled to a fresh air intake conduit 22. A turbine 24 of theturbocharger 18 is mechanically coupled via a rotational drive shaft 26to the compressor 16 in a conventional manner. An exhaust gas inlet ofthe turbine 24 is fluidly coupled to an exhaust manifold 28 of theengine 12 via an exhaust gas conduit 30. An exhaust gas outlet of theturbine 24 is fluidly coupled to an exhaust gas conduit 32.

In the illustrated embodiment, an exhaust gas aftertreatment system 34includes a conventional oxidation catalyst (OC) 34 that is disposedin-line with the exhaust gas conduit 32. The oxidation catalyst 36includes a conventional catalyst element responsive to hydrocarbonsintroduced into the exhaust gas stream to elevate the temperature of theexhaust gas to a temperature suitable for regeneration of one or moredownstream exhaust gas aftertreatment components. One such downstreamexhaust gas component illustrated in FIG. 1 comprises a NOx adsorbercatalyst (NAC) 36. The exhaust gas aftertreatment may further, but needno, include a conventional particulate filter 38 as shown in phantom inFIG. 1. It will be understood that the exhaust gas aftertreatment systemillustrated in FIG. 1 may include additional exhaust gas aftertreatmentcomponents. It will also be understood that the system 10 may, but neednot, include the turbocharger 18, and turbocharger 18 is accordinglyillustrated in FIG. 1 as being surrounded by a dashed-line block.

The system 10 further includes a control circuit 40 configured tocontrol the overall operation of the engine 12. In one embodiment, thecontrol circuit 40 is a microprocessor-based control circuit typicallyreferred to as an electronic or engine control module (ECM), orelectronic or engine control unit (ECU). It will be understood, however,that the control circuit 40 may generally be or include one or moregeneral purpose or application specific control circuits arranged andoperable as will be described hereinafter. The control circuit 40includes, or is coupled to, a memory unit 45 that stores therein anumber of software algorithms executable by the control circuit 40 tocontrol various operations of the engine 12.

The control circuit 40 includes a number of inputs configured to receivesensory data corresponding to one or more operating parameters of theexhaust gas aftertreatment system, and a number of outputs configured tocontrol one or more actuators. For example, the exhaust gasaftertreatment system includes a conventional oxygen sensor (also knownas a lambda sensor) 54 that is disposed in fluid communication with theexhaust gas conduit 32 between the NAC 36 and the particulate filter 38,if included in the aftertreatment system, and otherwise between theexhaust gas outlet of the NAC 36 and ambient. The oxygen sensor 54 iselectrically connected to an input of the control circuit 40 via asignal path 56, and is configured to produce a signal on the signal path56 corresponding to the oxygen concentration of the exhaust gas exitingthe NAC 36. The exhaust gas aftertreatment system may further includeanother oxygen sensor 50 that is disposed in fluid communication withthe exhaust gas conduit 32 between the OC 34 and the NAC 36 as shown inphantom in FIG. 1. If included in the exhaust gas aftertreatment system,the oxygen sensor 50 is electrically connected to another input of thecontrol circuit 40, and is configured to produce a signal on the signalpath 52 corresponding to the oxygen concentration of the exhaust gasentering the NAC 36. In alternative embodiments, the memory unit 45 mayinclude one or more conventional software algorithms executable by thecontrol circuit 40 to estimate the oxygen concentration of the exhaustgas entering the NAC 36, and in such embodiments the oxygen sensor 50may be omitted.

A conventional fuel system 58 is coupled to the engine 12, and iselectrically connected to the control circuit 42 via a number, N, ofsignal paths 60, wherein N may be any positive integer. The controlcircuit 40 includes conventional fueling logic which is responsive to anumber of engine operating conditions to determine appropriate fuelingcommands in a conventional manner. The control circuit 40 provides thefueling commands (FC) to the fuel system 58 via the one or more signalpaths 60 to thereby control the fuel system 58 in a conventional mannerto supply fuel to the engine 12.

It will be understood that the system 10 may include other conventionalcomponents, and in particular the engine 12 may have one or more airhandling components and/or sub-systems coupled thereto as is known inthe art. Examples of such one or more air handling components and/orsub-systems may include, but should not be limited to, a conventionalturbocharger, one or any combination of a conventional electronicallycontrollable exhaust gas recirculation (EGR) system, a conventionalelectronically controllable intake air throttle, a conventionalelectronically controllable exhaust gas throttle, an electronicallycontrollable variable geometry turbocharger, a conventionalelectronically controllable wastegate configured to selectively routeexhaust gas around a turbocharger turbine, and the like.

The memory unit 45 of the control circuit 40 includes a number ofconventional software algorithms to control operation of the fuel system58 under different operating conditions. For purposes of thisdisclosure, lean fuel operation of the engine 12 is defined as anair-to-fuel ratio of the air-fuel mixture supplied to the engine 12 thatis greater than the stoichiometric ratio for the particular fuel beingused. Rich fuel operation of the engine 12, in contrast, is defined asan air-to-fuel ratio of the air-fuel mixture supplied to the engine 12that is less than the stoichiometric ratio for the particulate fuelbeing used. It is generally understood in the industry that lean andrich fuel operation of the engine 12 is typically referred to in termsof a parameter called “lambda” or “λ.” Lambda is defined as theair-to-fuel ratio of the air-fuel mixture that is normalized to unity atthe stoichiometric ratio for the fuel being used. Thus, lambda valuesgreater than unity generally correspond to lean fuel operation of theengine 12, and lambda values less than unity generally correspond torich fuel operation of the engine 12.

During normal operation of the engine 12, the control circuit 40 isoperable, under the direction of one conventional software algorithm, tocontrol the fuel system 58 to supply fuel for lean fuel operation of theengine 12. The NOx adsorber catalyst may typically require periodicregeneration to release and oxidize trapped NOx. During such NOxadsorber regeneration, the control circuit 40 is operable, under thedirection of a conventional NAC regeneration control algorithm 65 tocontrol the fuel system 58 to supply fuel for alternate rich fueloperation of the engine 12 and lean fuel operation of the engine 12, andto also control the fuel system 58 in a conventional manner to introducehydrocarbons in the form of unburned or partially burned fuel into theexhaust gas produced by the engine. The oxidation catalyst 34 isconfigured to react with the hydrocarbons according to a knownexothermic reaction to elevate the temperature of the exhaust gassupplied to the NOx adsorber catalyst 36 to a temperature range suitablefor regeneration of the NOx adsorber 36. The control circuit 40 executesthe software algorithm 65 to initiate and control regeneration of theNOx adsorber catalyst 36 in a conventional manner. For example, thesoftware algorithm 65 may define a conventional closed-loop controlstrategy for controlling the fuel system 58 to selectively supplyhydrocarbons to the exhaust gas in the form of unburned or partiallyburned fuel and to supply fuel in a periodic lean-to-rich andrich-to-lean fueling strategy as a function of the oxygen concentrationof the exhaust gas exiting the NOx adsorber catalyst 36. Alternativelyor additionally, the software algorithm 65 may define a conventionalclosed-loop control strategy for controlling the fuel system 58 toselectively supply hydrocarbons to the exhaust gas in the form ofunburned or partially burned fuel and to supply fuel in a periodiclean-to-rich and rich-to-lean fueling strategy as a function of theoxygen concentrations of the exhaust gas entering and exiting the NOxadsorber catalyst 36. Alternatively, the software algorithm 65 maydefine an open-loop control strategy for controlling the fuel system 58in a conventional open-loop manner to selectively supply hydrocarbons tothe exhaust gas in the form of unburned or partially burned fuel and tosupply fuel in a periodic lean-to-rich and rich-to-lean fuelingstrategy.

Referring now to FIG. 2, one illustrative embodiment 36′ of the NOxadsorber catalyst 36 is shown. The NOx adsorber catalyst 36′ includes ahousing 70 having an exhaust gas inlet 80 configured to receive exhaustgas supplied by the engine 12, and exhaust gas outlet 82 and a chamber84 defined between the exhaust gas inlet 80 and outlet 82. Aconventional NOx adsorber element 86 is positioned in the chamber 84with a front face 86A facing the exhaust gas inlet 80 of the housing 70and a rear face 86B facing the exhaust gas outlet 82 of the housing 70.The NOx adsorber element 86 may be of conventional construction and isconfigured to trap NOx therein during normal, lean fuel operation of theengine 12, and to release the trapped NOx and reduce the released NOx tonitrogen during rich fuel operation of the engine 12, i.e., duringregeneration of the NOx adsorber catalyst as described hereinabove.

A hydrocarbon trap 88 is also positioned within the chamber 84 of thehousing 70 with a front face 88A facing the rear face 86B of the NOxadsorber element 86 and a rear face 88B facing the exhaust gas outlet 82of the housing 70. The hydrocarbon trap 88 may comprise a conventionalsubstrate that is wash-coated with a suitable hydrocarbon trappingcoating such as a zeolite-containing material or other suitablecoating(s). The hydrocarbon trap 88 is configured to trap hydrocarbonsthat travel through, or slip past, the NOx adsorber element during therich fuel operation of the engine 12 so that the exhaust gas exiting theNOx adsorber catalyst 36′ has little or no hydrocarbon content duringrich fuel operation of the engine 12. The trapped hydrocarbons are thenoxidized by oxygen present in the exhaust gas during lean fuel operationof the engine 12 that follows rich fuel operation of the engine 12.While the hydrocarbon trap 88 traps hydrocarbons during rich fueloperation of the engine 12 as just described, it allows pass through ofCO and H₂. As such, inclusion of the hydrocarbon trap 88 should notadversely affect detection of a lean-to-rich lambda transition by thedownstream oxygen sensor 54 in the system 10. Moreover, since thehydrocarbon trap 88 should trap most or all of the hydrocarbons thatslip through the NOx adsorber element 86 during rich fuel operation, thedownstream oxygen sensor 54 is less likely than NOx adsorber catalyststhat do not have the hydrocarbon trap 88 to prematurely detect arich-to-lean lambda transition, thereby reducing the likelihood ofpremature ending of the regeneration event.

In the embodiment illustrated in FIG. 2, the rear face 86B of the NOxadsorber element 86 is in contact with the front face 88A of thehydrocarbon trap 88. In one embodiment, the hydrocarbon trap 88 may beattached to the NOx adsorber element 86 or vice versa. In an alternateembodiment, the NOx adsorber element 86 and the hydrocarbon trap 88 maybe of unitary construction. In still another embodiment 36″ of the NOxadsorber catalyst 36, as illustrated by example in FIG. 3, the rear face86B of the NOx adsorber element 86 may be separated from the front face88A of the hydrocarbon trap 88 by a gap 90. The width of the gap 90 mayvary to suit the application, although it will be understood thatnotwithstanding the width of the gap 90 the NOx adsorber element 86 andthe hydrocarbon trap 88 both reside in the chamber 84 defined within thehousing 70, and the gap 90 is generally not configured to modify theflow of exhaust gas through the chamber 84.

While the invention has been illustrated and described in detail in theforegoing drawings and description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly illustrative embodiments thereof have been shown and described andthat all changes and modifications that come within the spirit of theinvention are desired to be protected.

1. A NOx adsorber catalyst comprising: a housing defining an inlet at one end configured to receive exhaust gas produced by an internal combustion engine, an outlet at an opposite end and a chamber between the inlet and the outlet, a NOx adsorber element positioned in the chamber adjacent to the inlet of the housing, the NOx adsorber element configured to trap NOx in the exhaust gas during lean fuel operation of the engine, and to release the trapped NOx and reduce the released NOx to nitrogen during rich fuel operation of the engine, and a hydrocarbon trap positioned in the chamber between the NOx adsorber element and the outlet of the housing, the hydrocarbon trap configured to trap hydrocarbons that travel through the NOx adsorber element during the rich fuel operation of the engine, wherein the trapped hydrocarbons are oxidized by oxygen present in the exhaust gas during lean fuel operation of the engine following rich fuel operation.
 2. The NOx adsorber catalyst of claim 1 wherein the hydrocarbon trap is integral with the NOx adsorber element.
 3. The NOx adsorber catalyst of claim 1 wherein the hydrocarbon trap is attached to the NOx adsorber element.
 4. The NOx adsorber catalyst of claim 1 wherein the hydrocarbon trap is spaced apart from the NOx adsorber element within the chamber of the housing.
 5. The NOx adsorber catalyst of claim 1 wherein the hydrocarbon trap comprises a substrate wash-coated with a zeolite-containing material.
 6. A NOx adsorber catalyst comprising: a housing defining an inlet at one end configured to receive exhaust gas produced by an internal combustion engine, an outlet at an opposite end and a chamber between the inlet and the outlet, a NOx adsorber element positioned in the chamber, the NOx adsorber element including a first portion adjacent to the inlet of the housing and configured to trap NOx in the exhaust gas during lean fuel operation of the engine, and to release the trapped NOx and reduce the released NOx to nitrogen during rich fuel operation of the engine, and a second portion integral with the first portion with the first portion positioned between the inlet of the housing and the second portion, the second portion configured to trap hydrocarbons that travel through the first portion during the rich fuel operation of the engine, wherein the trapped hydrocarbons are oxidized by oxygen present in the exhaust gas during lean fuel operation of the engine following rich fuel operation.
 7. A NOx adsorber catalyst comprising: a housing defining an inlet at one end configured to receive exhaust gas produced by an internal combustion engine, an outlet at an opposite end and a chamber between the inlet and the outlet, a NOx adsorber element positioned in the chamber adjacent to the inlet of the housing, the NOx adsorber element configured to trap NOx in the exhaust gas during lean fuel operation of the engine, and to release the trapped NOx and reduce the released NOx to nitrogen during rich fuel operation of the engine, and a hydrocarbon trap separate from the NOx adsorber element and positioned in the chamber between the NOx adsorber element and the outlet of the housing, the hydrocarbon trap configured to trap hydrocarbons that travel through the NOx adsorber element during the rich fuel operation of the engine, wherein the trapped hydrocarbons are oxidized by oxygen present in the exhaust gas during lean fuel operation of the engine following rich fuel operation.
 8. The NOx adsorber catalyst of claim 7 wherein the hydrocarbon trap is attached to the NOx adsorber element.
 9. The NOx adsorber catalyst of claim 7 wherein the hydrocarbon trap is spaced apart from the NOx adsorber element within the chamber of the housing.
 10. A system for processing NOx present in exhaust gas produced by an internal combustion engine, comprising: a NOx adsorber catalyst having housing defining an inlet at one end that is configured to receive the exhaust gas, an outlet at an opposite end and a chamber between the inlet and the outlet, a NOx adsorber element positioned in the chamber adjacent to the inlet of the housing, the NOx adsorber element configured to trap NOx in the exhaust gas during lean fuel operation of the engine, and to release the trapped NOx and reduce the released NOx to nitrogen during rich fuel operation of the engine, and a hydrocarbon trap positioned in the chamber between the NOx adsorber element and the outlet of the housing, the hydrocarbon trap configured to trap hydrocarbons that travel through the NOx adsorber element during the rich fuel operation of the engine, a fuel system configured to supply fuel to the engine, and a control circuit including a memory having stored therein a set of instructions that are executable by the control circuit to control the fuel system to normally supply fuel for lean fuel operation of the engine, and to control the fuel system to supply fuel for alternate rich fuel operation of the engine and lean fuel operation of the engine to regenerate the NOx adsorber, wherein the hydrocarbons trapped in the hydrocarbon trap are oxidized by oxygen present in the exhaust gas during lean fuel operation of the engine following rich fuel operation.
 11. The system of claim 10 further comprising an oxidation catalyst positioned between the engine and the NOx adsorber, wherein the instructions stored in the memory include instructions that are executable by the control circuit to control the fuel system to introduce hydrocarbons in the form of unburned or partially burned fuel into the exhaust gas during regeneration of the NOx adsorber, the oxidation catalyst reacting with the introduced hydrocarbons to heat the exhaust gas supplied to the NOx adsorber to an elevated temperature suitable for regeneration of the NOx adsorber.
 12. The system of claim 10 wherein the hydrocarbon trap is integral with the NOx adsorber element.
 13. The system of claim 10 wherein the hydrocarbon trap is attached to the NOx adsorber element.
 14. The system of claim 1 wherein the hydrocarbon trap is spaced apart from the NOx adsorber element within the chamber of the housing.
 15. The system of claim 10 wherein the hydrocarbon trap comprises a substrate wash-coated with a zeolite-containing material.
 16. The system of claim 10 further comprising an oxygen sensor configured to produce an oxygen signal corresponding to an oxygen concentration of exhaust gas exiting the NOx adsorber catalyst, wherein the instructions stored in the memory include instructions that are executable by the control circuit to control the fuel system to supply fuel for alternate rich fuel operation of the engine and lean fuel operation of the engine to regenerate the NOx adsorber according to a closed-loop control strategy as a function of the oxygen concentration of exhaust gas exiting the NOx adsorber catalyst.
 17. The system of claim 16 further comprising means for determining an oxygen concentration of exhaust gas entering the NOx adsorber catalyst, wherein the instructions stored in the memory include instructions that are executable by the control circuit to control the fuel system to supply fuel for alternate rich fuel operation of the engine and lean fuel operation of the engine to regenerate the NOx adsorber according to the closed-loop control strategy further as a function of the oxygen concentration of exhaust gas entering the NOx adsorber catalyst. 